Pressurized container with a piston movable therein and a device for determination of the piston position in the pressurized container

ABSTRACT

A pressurized container ( 10, 50 ) provided with a piston ( 13, 51 ) which is movable in the longitudinal direction of the pressurized container, wherein an electrode is arranged for determination of the position of the piston ( 13, 51 ) in the pressurized container ( 10, 50 ), at least in the wall of the pressurized container ( 10, 51 ) of a measuring arrangement for measurement of changes of electrical alternating field produced with supply of electrical energy, characterized in that the electrode, which is arranged on the wall of the pressurized container ( 10, 50 ) made from a resin-impregnated, fiber-reinforced plastic material, comprises an electrical conductor ( 23 ) which is sewn or stitched to the base material of a planar arrangement ( 15 ) with a form at least partially surrounding an inner wall part ( 14 ), and wherein the other electrode of the measuring arrangement is formed with the piston ( 13, 51 ) or with another electrical conductor ( 20 ) sewn or stitched onto the base material in the circumferential direction of the pressurized container ( 10, 50 ).

The invention relates to a pressurized container which has a piston movable in the longitudinal direction of the pressurized container, wherein an electrode is arranged for determining the piston of the piston in the pressurized container at least on the wall of the pressurized container as a component of a change in the measuring arrangement of the changing field of the supply of electric energy produced by changing the position of the piston in the pressurized container.

A container which has generic characteristics is known from DE 198 17 961. To make it possible to determine the relevant position of a piston which is movable in the container in the longitudinal direction, the piston supports at least one electrically conductive electrode member, and at least one electrode layer is arranged on the container wall so that the electrode member of the piston and the electrode layer of the container form a differentially constructed sensor for capacitive measuring of lengths and of relative displacement, which can be applied to determination of the position of the piston.

Furthermore, it is known from DE 42 05 048 A1 that for completely digital measuring of the position of a piston in a hydraulic cylinder, a cylindrical measurement head can be used which is surrounded by a tubular scale and which is arranged in a bore of the piston. The measurement head, the scale and the piston are arranged coaxially to each other and they are axially movable relative to each other. The scale is provided with a coding pattern on its inner side and the measurement head is provided with a coding pattern on its cylindrical outer side, forming a capacitor whose capacity changes depending on the position of the piston, and the measurement quantity is utilized for the measurement of the position of the piston.

The application of such a measurement system is problematic in the case of a pressured container which is manufactured from a fiber-reinforced plastic when the corresponding pressurized container is designed to enable discharging and/or advance storage of pressurized fluid.

A similar pressure cylinder is known for example from U.S. Pat. No. 3,508,777 A. The corresponding pressurized container consists in its basic construction of an internal unit and of an external unit, which are respectively made of a fiber-reinforced plastic material, wherein the fibers in the inner unit and the fibers in the outer unit have a different orientation. Between the inner unit and the outer unit is arranged a sliding plane, so that the layers in the construction of the pressure cylinder located outside and inside of the sliding plane can be extended away from each other or pulled together. Both end caps which are axially attached to the middle section are integral components of the multilayered construction of the pressure cylinder.

In this respect, the objective of the invention is to provide a retractable device of the pressurized container for the determination of the position of the movable piston in the pressurized container for such a pressurized container, which is made of a fiber-reinforced plastic material and which can be constructed in a simple manner during the manufacturing process.

This objective is attained on the basis of preferred embodiments and modifications of the invention in accordance with the description of the patent claims which follows this description.

According to the basic concept of the invention, one electrode of the fiber-reinforced pressurized container is constructed in the form of a wall component, which is at least partially wrapped around a planar arrangement of applied base material consisting of an electrical conductor that is sewn or stitched onto the wall constructed from fibers impregnated with resin, and the other electrode of the measuring arrangement is formed by the piston or another electrical conductor, which is stitched or sewn in the circumferential direction of the pressurized container so that it is offset on the base material.

In this context, a method for manufacturing a base material to which an electrical conductor or electrical conductors are sewn or stitched is known from EP 1 923 680 A2. The signal structure manufactured in this manner is employed for the manufacturing of strain sensors, pressure sensors and/or breakage sensors.

An advantage connected with the invention is that for example a hydraulic cylinder which is produced from a fiber-reinforced plastic material can be manufactured with a lightweight construction. In the construction of the fiber-reinforced plastic can thus be integrated in an advantageous manner a base material onto which at least one electrical conductor is sewn or stitched, so that the electrical conductor which is thus constructed is incorporated in the wall of the pressure cylinder of the pressurized container, for example in a capacitively operating measuring arrangement, wherein an alternating electric field is created which covers the inner part of the pressurized container whose changes caused by the piston moving in the electric alternating field can be measured and transformed for determination of the position of the piston.

The measuring arrangement can according to an embodiment of the invention comprise an electrically conductive material, wherein the piston forms one electrode, and the electric conductor attached to the base material forms another electrode of the capacitive measuring arrangement. In this manner, the piston functions as a transmitter of electrical signals received by the electric conductor located on the base material which is used as a receiver. In this case, the piston can be constructed of an electrically conductive material, and the applied electrical signal is coupled through the reference potential of the measuring arrangement with the signal of the electrode deployed on the base material, while the piston is preferably made of aluminum.

As an alternative to this, the piston can consist of a material that is not electrically conductive so that an electrode connected to an energy supply is arranged in the piston, which is used for transmitting the desired signals from the piston.

Therefore, the electrode arranged in the piston, as well as the electrical or electronic circuits arranged in the piston which are powered by a long lasting battery, are thus connected. The battery thus supplies energy for the electronic circuit, which generates a signal and which is connected as a transmitting electrode to the electrode arranged in the piston. A similar arrangement is particularly suitable for a “floating” arrangement of the piston in a pressurized container, so that no piston rod that would be protruding from the pressurized container is provided.

An embodiment of a pressurized container which is constructed as a pressure cylinder supporting a piston with a protruding piston rod may be designed so that an electrode is located in the piston for supplying signals or energy for the electrode in the piston rod.

An effective embodiment of the invention can be also constructed so that a planar arrangement consisting of a base material is wrapped around an inner part of the wall of the pressurized container provided with a sewn or stitched electric conductor which is formed as a electrode with a meandering course, and the size of the meandering turns that is defined by the peaks and valleys in the longitudinal direction of the pressurized container changes the characteristic line in the circumferential direction of the pressurized container. This can be also constructed so that the size of the meandering turns is increased through a longitudinal extension of the pressurized container which is provided at the end of the pressurized container with a connection of the electrode to the measuring arrangement.

As an alternative to a measurement construction designed with a transmitter having an integrated piston, it is also possible to provide in an alternative embodiment an electrode of the measuring arrangement which is extended in the longitudinal direction of the pressurized container and on which a conductor is formed sewn or stitched onto the base material with a planar arrangement so that it is wrapped around an inner part of the wall, and the other electrode is formed also as a conductor with a meandering course which is sewn or stitched to the base material, wherein the size of the meandering valleys located in the longitudinal direction of the pressurized container changes in the circumferential direction of the pressurized container, and wherein both electrodes are arranged so that they are mutually shifted in the circumferential direction of the pressurized container and the capacitive coupling between the electrodes is increased with the movable piston in different circumferential regions of the electric conductor of the pressurized container.

The principle of the invention can be basically also applied as long as an inductive measuring arrangement is formed on a base material onto which is sewn or stitched at least one conductor as a component of the measuring arrangement; such an inductive measuring arrangement that is known for example from DE 102 50 846 A1.

With regard to the integration of the planar arrangement of a base material onto which electrical conductors are sewn or stitched into the jacket of the pressurized container, it is also possible to construct an embodiment of the invention in which the planar arrangement which is made of base material to which electrical conductors are sewn or stitched is wrapped around an inter layer consisting of a plastic material which is used as an inner wall part, so that at least one other layer made of a fiber-reinforced material is attached to the outer side of the planar arrangement, wherein it is possible for example to provide a planar arrangement consisting of the base material which is laminated onto the surface of the internal wall part of the pressurized container.

In order to construct an undisturbed alternating electric field permeating the inner part of the pressurized container, it is important that the inner layer contain either no reinforcing fibers, or at least no electrically conductive fibers. In this respect, it is possible to use an inner layer which is provided with a reinforcement consisting of fibers which are not electrically conductive.

While in particular the use of carbon fibers as a reinforcement increases the strength of the pressurized container, it is necessary to ensure that when carbon fibers are used in the outer layer, they will not be contacted between the electrically conductive carbon fibers and the conductors located on the arrangement. The design of the invention therefore in this respect provides an intermediate layer, which is made of electrically insulating material and which is located between the planar arrangement made of the base material and the outer layer surrounding this material.

Since it is also necessary to use material which is not electrically conducive for the reinforcement of the outer layer, care is taken in an alternative embodiment of the invention to create also the construction of an outer electric shield to ensure that either additional conductive fibers are employed in the outer layer, or so that a shield consisting of an electrically conductive material is deposited on the outer periphery of the container.

The drawings show embodiments of the invention described below, which indicate:

FIG. 1 a pressurized container provided with a piston arranged therein in a cut-open representation indicating the principle of the invention,

FIG. 2 a pressurized container constructed as a pressure cylinder provided with a piston rod which is guided out of the pressure cylinder in a representation according to FIG. 1,

FIG. 3 a pressurized container having a piston which is movable therein, as well as a planar arrangement provided with at least one electric conductor sewn or stitched onto the base material arranged in the wall of the pressurized container,

FIG. 3 a a representation of the planar arrangement according to FIG. 3 a, consisting of the base material on which two electrical conductors are sewn or stitched in a developed representation,

FIG. 3 b the planar arrangement according to FIG. 3 a in an alternative embodiment,

FIG. 3 c the planar arrangement according to FIG. 3 a or 3 b in another embodiment.

First, FIG. 1 shows the construction of a pressurized container 10 consisting of a fiber-reinforced plastic material. The pressurized container 10 is provided with a piston chamber 12 surrounded by a wall 11, wherein a piston 13 is movable in the piston chamber 13. The pressurized container 10 is equipped with a capacitively functioning measuring arrangement through which each position of the piston 13 inside the piston chamber 12 of the pressure container 10 can be detected.

A planar arrangement 15, which is provided as a structural component of the capacitive measuring arrangement, consists of at least one electrical conductor sewn or stitched to the base material, which is integrated in the pressurized container 10. The planar arrangement 15 is wrapped around an inner wall part 14 which consists of a fiber-reinforced plastic material, wherein at least one other layer 16 consisting of a fiber-reinforced material is applied externally onto the planar arrangement.

In FIG. 2 is depicted a corresponding representation of a pressure cylinder 50 having a piston 51, and a piston 52 rod which is carried by the cylinder and guided out of the pressure cylinder 50.

The planar arrangement 15 belonging to embodiments of the pressurized container 10 or of the pressure cylinder 50 indicated in FIGS. 1 and 2 consists of at least one electric conductor sewn or stitched to base material indicated in a developed top view shown in FIG. 3 a. In this case, a first electrode located on the planar arrangement 15 consists of a conductor 20 extended in the longitudinal direction of a container 10, which is represented by way of an example and provided with a forward line 21, as well as with a return line 22. The return line is not required for the construction of the capacitive measuring arrangement and it is provided here only for technical processing reasons relating to the manufacturing of the planar arrangement 15 to which is sewn or stitched an electrical conductor. During the manufacturing of the planar arrangement 15, the sewing or stitching head is guided in the forward direction and in the return direction through the base material so that a manufactured section of the corresponding sewing or stitching head will be available at the end without an interruption in the sewing or stitching operation in its starting position for the manufacturing of a new planar arrangement. In this respect, the end of the forward line 21 is connected through a corresponding connection line 17 with a measuring and evaluation device 18 which is arranged outside of the pressurized container 10.

The second electrode attached to the same planar arrangement 15 also consists of a base material provided with a sewn or stitched conductor 23, which also comprises a forward line 24 and a return line 25. The conductor 23 having the forward line 24 and the return line 25 is thus attached onto the planar arrangement 15 with a meandering course,

wherein the defined size of the meandering turns is changed depending on the peaks 26 and the valleys 27 of the characteristic line 28 running through the pressurized container 10, namely so that it is increased starting from the lower connection side in the upward direction of the measuring and evaluating device. The end of the forward line 24 of the meandering conductor 23 is also connected through a connection line 17 to the measuring and evaluating device 18.

When a corresponding signal is applied, this will result in transmission of signal between electrical conductors 20, 23 of both planar arrangements and of the planar arrangement 15 integrated in the wall 11 of the pressurized container 10, which are mutually shifted in the circumferential direction of the pressurized container according to the frequency of the applied signal amplitude. Due to the piston 13 which is coupled and moved between both conductors 20, 23, a measurable change of the generated signal is created, so that the signal which is transmitted from the electrode 20 depending on the coverage of the conductor 23 serving as a reception antenna will be received as a stronger or weaker signal depending on the piston 13. The corresponding measurement results will be then converted in the measurement and evaluation device 18 into the confirmation of the position of the piston 13 in the pressurized container 10.

FIGS. 3 b and 3 c illustrate an embodiment of the invention, wherein only one conductor 23 having a meandering form is attached to the planar arrangement 15. In this case, the piston 13 itself serves as a transmitter, so that the signal received by the conductor 23 will again have a stronger or weaker amplitude depending on the coverage of the piston 13 and of the conductor 23. As long as voltage supply is provided for the piston 13, in case of a further development of the piston rod which is projecting on one side from the pressurized container 10, supplying of signals can be performed through the piston rod. As an alternative to this, a battery having a long life can be arranged in the piston 13.

The result of the different determinations of the meandering turns, which can be seen in FIGS. 3 b and 3 c of each conductor 23, and which in FIG. 35 is a linear characteristic line used for the determination of the distance to the piston 13 from the lower end of the measurement and evaluation device 18 which is facing the pressurized container 10. This can be achieved as long as the meandering form of the conductor 23 in the area of the smallest size of the meandering turns also determines a small coverage with the piston.

Although this is not further illustrated in detail in the drawing, it is clear from the formation of the layer creating the inner wall part 14 that care must be taken so that in the case when fiber reinforcement is used therein, no electrically conductive fibers will be employed because otherwise the capacitive arrangement would not be functional. That is why when the outer layer 16 which is used for reinforcement of the jacket of the pressurized container 10 is created in particular with the application of carbon fibers, since carbon fibers are electrically conductive, it is necessary to prevent contact between the carbon fibers in the inner wall part 14 and the conductors 20, 23 which are located in the planar arrangement 15 of the outer layer 16. That is why an intermediate layer which is made of electrically insulating material should be arranged between the planar arrangement 15 and the outer layer 16.

Since other influences could also interfere with the capacitive measuring arrangement, in the case when carbon fibers are used as a reinforcement in the outer layer 16, these carbon fibers also create electrical shielding. If non-conductive fibers are used for reinforcement in the outer layer 16, it is necessary to ensure that that a similar electrical shield is additionally used. This can be done by including electrically conductive fibers in the outer layer 16, or by encasing the outer layer 16 of the pressurized container 10 in an electrically conductive material.

In all the cases, the outer layer or the outer shield must be connected to the electrical potential of the measuring arrangement, or to another electrical potential.

The characteristics disclosed in the description above as well as in the patent claims and in the drawings can be used individually or in any combinations which can be substantial for the realization of the invention in their different embodiments. 

1. A pressure vessel having a piston movable in a longitudinal direction of the pressure vessel, such that for determining the position of the piston in the pressure vessel, an electrode is arranged, at least on the wall of the pressure vessel, as a constituent of a measurement arrangement measuring the change, generated by the change in the position of the piston in the pressure vessel, in an alternating electric field generated by the delivery of electrical energy, wherein the electrode arranged on the wall of the pressure vessel, which latter is constructed from resin-impregnated fibers and is made of fiber-reinforced plastic, is made up of an electrical conductor sewn or stitched onto a base material applied in the form of a planar arrangement at least partly wrapping around an inner wall part, and the other electrode of the measurement arrangement is constituted by the piston or by a further electrical conductor stitched or sewn onto the base material with an offset in the circumferential direction of the pressure vessel.
 2. The pressure vessel according to claim 1, wherein in the context of a capacitive measurement arrangement, the piston is made of an electrically conductive material and is coupled, via the reference potential of the measurement arrangement, to the signal of the electrode present on the base material.
 3. The pressure vessel according to claim 1, wherein in the context of a capacitive measurement, the piston is made of an electrically non-conductive material, and an electrode connected to an energy supply is arranged in the piston.
 4. The pressure vessel according to claim 3, wherein the piston is carried at least on one side by a piston rod guided out of the pressure vessel embodied as a pressure cylinder, and a signal infeed or energy infeed for the electrode present in the piston is arranged in the piston rod.
 5. The pressure vessel according to claim 1, wherein the electrical conductor sewn or stitched onto the planar arrangement of base material wrapped around an inner wall part of the pressure vessel is embodied as an electrode having a serpentine profile, and the size of the serpentine turns, defined by the elevations and the valleys located on a baseline extending in a longitudinal direction of the pressure vessel, changes in the circumferential direction of the pressure vessel.
 6. The pressure vessel according to claim 5, wherein the size of the serpentine turns increases, proceeding from that end of the pressure vessel which comprises the connection of the electrode to the measurement arrangement, over the longitudinal extension of the pressure vessel.
 7. The pressure vessel according to claim 1, wherein the one electrode of the measurement arrangement is constituted by a conductor, extending in a longitudinal direction of the pressure vessel, sewn or stitched onto the planar arrangement of base material wrapped around an inner wall part of the pressure vessel, and the other electrode is constituted by a conductor having a serpentine profile and likewise sewn or stitched onto the base material, such that the size of the serpentine turns, defined by the elevations and the valleys located on a baseline extending in a longitudinal direction of the pressure vessel, changes in the circumferential direction of the pressure vessel, and such that the two electrodes are arranged on the base material with an offset from one another in the circumferential direction of the pressure vessel, and the piston, movable between the electrical conductors located in different circumferential regions of the pressure vessel, intensifies the capacitive coupling between the electrodes.
 8. The pressure vessel according to claim 1, wherein a planar arrangement, applied onto the wall of the pressure vessel and made of a base material sewn or stitched to at least one electrical conductor, forms a constituent of an inductive measurement arrangement, and the change, generated by the change in the position of the piston in the pressure vessel, in an electric field generated by the delivery of electrical energy is measured in the measurement arrangement, and the respective position of the piston in the pressure vessel is determined therefrom.
 9. The pressure vessel according to claim 1, wherein the planar arrangement made of the base material sewn or stitched to the electrical conductors is wrapped around an inner layer, made of plastic, as an inner wall part, and at least one further layer of a fiber-reinforced plastic is applied externally onto the planar arrangement.
 10. The pressure vessel according to claim 9, wherein the inner layer is equipped with a reinforcement made of electrically non-conductive fibers.
 11. The pressure vessel according to claim 9, wherein the planar arrangement made of base material is laminated onto the surface of the inner wall part.
 12. The pressure vessel according to claim 1, wherein the outer layer is equipped with a reinforcement made of carbon fibers, and an intermediate layer of an insulating material is arranged between the planar arrangement made of the base material and the outer layer that wraps around it.
 13. The pressure vessel according to claim 1, wherein the outer layer is equipped with a reinforcement made of electrically non-conductive fibers, and electrically conductive fibers are additionally introduced into the outer layer in order to constitute a shield.
 14. The pressure vessel according to claim 1, wherein the outer layer is equipped with a reinforcement made of electrically non-conductive fibers, and a shield made of an electrically conductive material is applied onto the outer periphery of the pressure vessel. 